The negative effects of inbreeding (higher occurrence of genetic defects, inbreeding depression…) are well known by breeds’ managers. However we still have a poor insight of how the genome is impacted by inbreeding. For over a 200 years period, a French sheep breed called the Rambouillet has been kept in a single flock without any introgression. Pedigree information was fully recorded since the 1870s. For the last fifty years, minimizing the breed’s inbreeding level has been the only goal of its management plan. It reached 52% for nowadays animals according to simulation data based on pedigrees. Despite this level, the breed’s weight, prolificacy and fertility have not changed over the last forty years. Altogether this breed gives a unique opportunity to explore the consequences of inbreeding at the genome level. To do so, we used a high density chip (600 K SNP) on a panel of 46 individuals. Among these animals, 38 were born between 2006 and 2012, and eight are older males born in the 1980s whose samples come from the French National Cryobank. First results showed that the genome of the breed was highly structured with a very low level of diversity. However the genomic inbreeding level based on run of homozygosity (ROH) was about half the estimation based on pedigree information, and a very weak inbreeding depression was detected. Therefore, we investigated more precisely at the chromosome level for ‘cold spots’ of diversity based on ROH. When compared with two related breeds, the Mourerous and the Arles, the Rambouillet showed much more ROH segments, but the total length of ROH is actually lower than expected. Linkage disequilibrium (LD) was also calculated at chromosome level and the genome structure appeared to differ between each chromosome. This information suggests a mutational load purge that occurred throughout the years. Ongoing research seems to confirm this hypothesis since hot spots of diversity are found in regions with genes involved in major development patterns (such as cells division). Finally, the Rambouillet sheep proves to be a valuable source of investigation in the understanding the genome aspects of inbreeding.